Land Rover Repair: land rover discovery 91, land rover discovery, low voltage wiring

Question
I hatve landrover discovery 1991 3.5L petrol, have replacced spark plugs and fuel filter and starts sometimes and runs well when it does, but seams to be not sparking properly...suggestions??

Answer
If you are correct about the "not sparking properly," you should be loking at the other ignition components.  Check the cap, rotor, wires.  Check the coil wire.  Check the coil itself for signs of oil leakage (they are oil filled.)  Check the low voltage wiring to the coil.  Finally, you can look at the pickup and module on the distributor, though in my experience they don't become "weak" they just fail 100% or work 100%. In a 1991, those are all the components that affect spark quality.